1. Field of the Invention
The present invention relates to an electronic apparatus. In particular, the invention relates to a printed circuit board unit including a printed circuit board and an electronic circuit component mounted on the surface of the printed circuit board.
2. Description of the Prior Art
For example, a printed circuit board unit often includes a power source layer and a ground layer formed within a printed circuit board, as disclosed in Japanese Patent Application Publication No. 9-27692. A connector is mounted on the surface of the printed circuit board at a first section. An IC (Integrated Circuit) chip is likewise mounted at a second section. Signal line patterns are utilized to connect the connector to the IC chip. The power source and ground layers are formed at locations off the first section in the printed circuit board unit. The signal line patterns can thus be protected from noise transmitted from the power source and ground layers to the utmost.
A noise cut filter such as a transformer is mounted on the surface of the printed circuit board in the aforementioned printed circuit board unit between the connector and the IC chip. The transformer is located on a third section defined between the first and second sections. The power source and ground layers are formed in the third section. If the transformer is exposed within a larger noise transferred from the power source and ground layers, the transformer cannot sufficiently remove the noise. The noise tends to reach the connector through the signal line pattern. A so-called electromagnetic interference, EMI, must occur between the connector and any outside equipment.